VPN to Windows Server 2003

Hello,
Our first mac user is attempting to connect to our servers via VPN. His machine has MAC OS X and is using VPN Client Darwin 4-91.01.0080. They are able to successful connect, but none of the network drives pop-up on his desktop, and when he attempts to "connect to server" he gets the message:
"Server May Not Exist or Is Not Operational At this Time". My boss and I are clueless as to what to do considering 99.9 percent of the machines on our network use Windows machines. Any help would be greatly appreciated!
-B